need to get more run out of a lazy horse. Ran a blood  test, all good.  Any suggestions?

Make it fun. Breeze him. Find somewhere long with good footing and let him rip. Take a friend on a horse that does like to run. Race them. Take him to a nearby track and get an exercise rider to breeze him. Use the same cue every single time you want to step on the gas. A noise. A whistle. Something the horse will relate to speed.